Estimation device, power storage device, and estimation method

Abstract

To provide an estimation device for improving the estimation accuracy of cumulative error by a current integration method.SOLUTION: An estimation device for estimating a residual electricity quantity of a power storage cell or a battery pack executes: first processing for estimating a residual electricity quantity based on a cumulative value of a current of the power storage cell or the battery pack; second processing for estimating a cumulative error of the residual electricity quantity based on the cumulative value of a measurement error of the current; third processing for estimating the residual electricity quantity by a method different from the first processing; fourth processing for calculating a residual electricity quantity difference that is the difference between the residual electricity quantity estimated in the first processing and the residual electricity quantity estimated in the third processing; and fifth processing for calculating a correction value of the measurement error based on the cumulative error and the residual electricity quantity difference.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a technique for correcting a measurement error of a current and improving the accuracy of estimating the remaining amount of electricity in a storage cell or a battery pack. [Background technology]

[0002] There is known a technique for measuring the current and voltage of a storage cell or a battery pack and estimating the remaining amount of electricity in the storage cell or the battery pack from the measurement results (for example, Patent Document 1 listed below). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-283922 A Summary of the Invention [Problem to be solved by the invention]

[0004] One method for estimating the remaining charge of a storage cell or a battery pack is the current integration method, in which errors caused by measurement errors contained in the current measurement value are accumulated in the estimation result (hereinafter, such errors accumulated in the estimation result of the remaining charge are referred to as "accumulated errors").

[0005] The present invention discloses a technique for obtaining a correction value for a current measurement error and improving the estimation accuracy of an accumulated error. [Means for solving the problem]

[0006] An estimation device that estimates the remaining amount of electricity in a storage cell or a battery pack executes a first process of estimating the remaining amount of electricity based on an integrated value of a current of the storage cell or the battery pack, a second process of estimating a cumulative error of the remaining amount of electricity based on an integrated value of a measurement error of the current, a third process of estimating the remaining amount of electricity by a method different from the first process, a fourth process of calculating a remaining amount of electricity difference that is the difference between the remaining amount of electricity estimated by the first process and the remaining amount of electricity estimated by the third process, and a fifth process of calculating a correction value for the measurement error based on the cumulative error and the remaining amount of electricity difference.

[0007] Examples of the "remaining amount of electricity" include the remaining capacity [Ah] of a storage cell or a battery pack, and SOC (State of Charge) [%].

[0008] The present invention can be applied to a power storage device, and can also be applied to a method for estimating the remaining amount of electricity in a power storage device, and a program for estimating the remaining amount of electricity. Effect of the Invention

[0009] According to this configuration, it is possible to obtain a correction value for a measurement error of a current flowing through the power storage cell or the battery pack. By correcting the measurement error based on the correction value, it is possible to improve the estimation accuracy of the cumulative error. [Brief description of the drawings]

[0010] [Figure 1] Car side view [Diagram 2] Exploded perspective view of the battery [Diagram 3] Plan view of a secondary battery cell [Figure 4] Cross section of line AA in Figure 3 [Diagram 5] Block diagram showing the electrical configuration of a vehicle [Figure 6] Block diagram showing the electrical configuration of the battery [Figure 7] Current waveform near full charge [Figure 8] A diagram showing the relationship between SOC transition and current integration time [Figure 9] Flowchart of SOC estimation process [Figure 10] Diagram showing SOC estimation range [Figure 11] SOC-OCV correlation characteristics of secondary battery cells DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] <Outline of the estimation device> (1) An estimation device that estimates the remaining amount of electricity in a storage cell or a battery pack executes a first process that estimates the remaining amount of electricity based on an integrated value of a current of the storage cell or the battery pack, a second process that estimates a cumulative error of the remaining amount of electricity based on an integrated value of a measurement error of the current, a third process that estimates the remaining amount of electricity by a method different from the first process, a fourth process that calculates a remaining amount of electricity difference, which is the difference between the remaining amount of electricity estimated in the first process and the remaining amount of electricity estimated in the third process, and a fifth process that calculates a correction value for the measurement error based on the cumulative error and the remaining amount of electricity difference.

[0012] In this configuration, the remaining amount of electricity is estimated based on the integrated value of the current of the storage cell or the battery pack (first process), and the accumulated error of the remaining amount of electricity is estimated based on the integrated value of the measurement error of the current (second process). The measurement error is an arbitrary value set based on a statistical value or an experimental value instead of the true value of the error, which is difficult to measure directly.

[0013] The remaining amount of electricity in the storage cell or battery pack is estimated using a method different from the first process (third process). A remaining amount of electricity difference, which is the difference between the remaining amount of electricity estimated in the first process and the remaining amount of electricity estimated in the third process, is calculated (fourth process). The remaining amount of electricity estimated in the third process is not based on an integrated value of the current, and therefore does not include an error caused by the current. Therefore, the remaining amount of electricity difference calculated in the fourth process reflects a value obtained by accumulating errors caused by the current.

[0014] The errors caused by the current include gain error and offset error. Since the gain error is offset by repeated charging and discharging, it is necessary to reduce the effect of the offset error in order to improve the accuracy of estimating the remaining amount of electricity. The remaining amount of electricity difference calculated in the fourth process includes the cumulative value of the offset error.

[0015] A correction value for the measurement error is calculated based on the cumulative error and the remaining electric quantity difference thus obtained (fifth process). By calculating the correction value for the measurement error, it is possible to determine whether the value of the measurement error used in the second process is appropriate. For example, if the calculated correction value is small enough to be ignored, it can be determined that the value of the measurement error used in the second process is appropriate and the accuracy of the cumulative error estimated based on the measurement error is sufficiently high. If the calculated correction value is very large, it can be determined that the value of the measurement error used in the second process is inappropriate and requires correction, or that there is a possibility of an abnormality occurring in the current measurement circuit, etc.

[0016] (2) The measurement error may be corrected based on the correction value calculated in the fifth process (sixth process), and the second process may be executed using the corrected measurement error after execution of the sixth process. With this configuration, the value of the measurement error can be brought closer to the true value by the correction, improving the estimation accuracy of the cumulative error. When the estimation accuracy of the cumulative error is improved, the estimation accuracy of the remaining amount of electricity in the storage cell or the assembled battery based on the integrated value of the current is improved. This allows the remaining amount of electricity in the storage cell or the assembled battery to be estimated with high accuracy, so that the battery performance of the storage cell or the assembled battery can be utilized to the maximum.

[0017] (3) The estimation device may execute the sixth process to correct the measurement error when the difference between the accumulated error and the remaining charge difference exceeds a threshold value. When the difference between the accumulated error and the remaining charge difference is large, it is assumed that the accumulated error, which is the accumulated value of the measurement errors, is large. Specifically, this is the case when the accumulated error becomes large as a result of setting the measurement error to a value larger than the true value. By executing the sixth process and correcting the measurement error, the measurement error can be brought closer to the true value. This improves the estimation accuracy of the remaining charge of the storage cell or the battery pack based on the integrated value of the current, and makes it possible to make the most of the battery performance of the storage cell or the battery pack.

[0018] (4) In the third process, the remaining amount of electricity in the storage cell or the assembled battery may be estimated by a full charge detection method in which the storage cell or the assembled battery is charged until the storage cell or the assembled battery is fully charged.

[0019] The remaining charge estimated by the full charge detection method does not include accumulated current measurement errors, and therefore has higher estimation accuracy than the remaining charge estimated based on the integrated current value. Based on the remaining charge estimated by the full charge detection method, the remaining charge estimated in the first process can be corrected with high accuracy in the fourth process. As a result, a highly accurate correction value can be obtained in the fifth process.

[0020] (5) The energy storage device includes an energy storage cell or an assembled battery, a current measuring unit that measures a current of the energy storage cell or the assembled battery, and the estimation device. The estimation device improves the accuracy of estimating the remaining amount of electricity in the energy storage cell or the assembled battery, thereby making it possible to make the most of the performance of the energy storage cell or the assembled battery.

[0021] <Embodiment 1> 1. Battery Description FIG. 1 is a side view of automobile 10, and FIG. 2 is an exploded perspective view of battery 50. Automobile 10 is an engine-driven vehicle and is equipped with battery 50. Automobile 10 may be equipped with a power storage device or a fuel cell as a vehicle drive device instead of an engine (internal combustion engine). FIG. 1 shows only automobile 10, engine 20, and battery 50, and other parts that make up automobile 10 are not shown. Automobile 10 is an example of a "vehicle", and battery 50 is an example of an "power storage device".

[0022] As shown in FIG. 2, the battery 50 includes a battery pack 60, a circuit board unit 65, and a container 71.

[0023] The container 71 includes a main body 73 and a lid 74 made of a synthetic resin material. The main body 73 is cylindrical with a bottom. The main body 73 includes a bottom portion 75 and four side portions 76. An upper opening 77 is formed at the upper end portion by the four side portions 76.

[0024] The container 71 houses the battery pack 60 and the circuit board unit 65. In the embodiment shown in FIG. 2, the battery pack 60 has twelve secondary battery cells 62. The secondary battery cells 62 are an example of "power storage cells." The twelve secondary battery cells 62 are connected in three parallel connections and four in series. The circuit board unit 65 is disposed on top of the battery pack 60. In the block diagram of FIG. 6 described later, the three secondary battery cells 62 connected in parallel are represented by one battery symbol.

[0025] The lid 74 shown in Fig. 2 closes an upper opening 77 of the main body 73. An outer peripheral wall 78 is provided around the lid 74. The lid 74 has a protruding portion 79 that is generally T-shaped in plan view. The positive external terminal 52 is fixed to one corner of the front portion of the lid 74 (the front left side in Fig. 2), and the negative external terminal 51 is fixed to the other corner.

[0026] 3 and 4, the secondary battery cell 62 is configured by housing an electrode assembly 83 together with a non-aqueous electrolyte in a rectangular parallelepiped case 82. The secondary battery cell 62 in this embodiment is a lithium ion secondary battery. The case 82 has a case body 84 and a lid 85 that closes the upper opening.

[0027] The secondary battery cell 62 is not limited to the prismatic cell shown in FIG. 3 and FIG. 4, but may be a cylindrical cell or a pouch cell having a laminate film case.

[0028] The electrode body 83 is formed by disposing a separator made of a porous resin film between a negative electrode element in which an active material is applied to a substrate made of, for example, copper foil, and a positive electrode element in which an active material is applied to a substrate made of aluminum foil. Both of these are strip-shaped, and are wound flatly so that they can be housed in the case body 84, with the negative electrode element and the positive electrode element shifted to opposite sides in the width direction relative to the separator.

[0029] The electrode body 83 may be of a laminated type instead of a wound type.

[0030] A positive electrode terminal 87 is connected to the positive electrode element via a positive electrode current collector 86, and a negative electrode terminal 89 is connected to the negative electrode element via a negative electrode current collector 88 (see FIG. 4). The positive electrode current collector 86 and the negative electrode current collector 88 each comprise a flat base portion 90 and legs 91 extending from the base portion 90. A through hole is formed in the base portion 90. The legs 91 are connected to the positive electrode element or the negative electrode element.

[0031] The positive electrode terminal 87 and the negative electrode terminal 89 each comprise a terminal body 92 and a shaft 93 that protrudes downward from the center of the lower surface of the terminal body 92. Of these, the terminal body 92 and shaft 93 of the positive electrode terminal 87 are integrally formed from aluminum (a single material). In the negative electrode terminal 89, the terminal body 92 is made of aluminum, and the shaft 93 is made of copper, and these are assembled together. The terminal body 92 of the positive electrode terminal 87 and the negative electrode terminal 89 are disposed on both ends of the lid 85 via gaskets 94 made of an insulating material, and are exposed to the outside from the gaskets 94.

[0032] The lid 85 has a pressure relief valve 95. As shown in Fig. 3, the pressure relief valve 95 is located between the positive electrode terminal 87 and the negative electrode terminal 89. The pressure relief valve 95 opens to reduce the internal pressure of the case 82 when the internal pressure of the case 82 exceeds a limit value.

[0033] FIG. 5 is a block diagram showing the electrical configuration of the automobile 10, and FIG. 6 is a block diagram showing the electrical configuration of the battery 50. As shown in FIG.

[0034] As shown in FIG. 5, the automobile 10 includes an engine 20 as a drive device, an engine control unit 21, an engine starting device 23, an alternator 25 as a vehicle generator, an electric load 27, a vehicle ECU (Electronic Control Unit) 30, and a battery 50.

[0035] The battery 50 is connected to the power line 37. The engine starting device 23, the alternator 25, and the electric load 27 are connected to the battery 50 via the power line 37.

[0036] The engine starting device 23 includes a starter motor. When the ignition switch 24 is turned on, a cranking current flows from the battery 50 to drive the engine starting device 23. The driving of the engine starting device 23 rotates the crankshaft, and the engine 20 can be started.

[0037] The electric load 27 is an electric load mounted on the automobile 10 other than the engine starting device 23. The electric load 27 has a rated voltage of 12 V, and is an air conditioner, an audio system, a car navigation system, an auxiliary device, or the like.

[0038] The alternator 25 is a vehicle generator that generates electricity using the power of the engine 20. When the amount of electricity generated by the alternator 25 exceeds the amount of electricity consumed by the electrical load of the automobile 10, the battery 50 is charged by the alternator 25. When the amount of electricity generated by the alternator 25 is less than the amount of electricity consumed by the electrical load of the automobile 10, the battery 50 discharges to make up for the shortage of electricity generated.

[0039] The vehicle ECU 30 is communicatively connected to the battery 50 via a communication line M1, and is communicatively connected to the alternator 25 via a communication line M2. The vehicle ECU 30 receives SOC information from the battery 50, and controls the amount of power generation of the alternator 25, thereby controlling the SOC of the battery 50.

[0040] The vehicle ECU 30 is communicatively connected to the engine control unit 21 via a communication line M3. The engine control unit 21 is mounted on the automobile 10, and monitors the operating state of the engine 20.

[0041] The engine control unit 21 monitors the running state of the automobile 10 based on the measured values ​​of instruments such as a speedometer. The vehicle ECU 30 obtains from the engine control unit 21 information on the on / off state of the ignition switch 24, information on the operating state of the engine 20, and information on the running state of the automobile 10 (running, stopped, idling stop, etc.).

[0042] 6, the battery 50 includes a current interruption device 53, a battery pack 60, a current measurement unit 54, a temperature sensor 58, and a management device 100. The battery 50 is a rated 12V battery.

[0043] The current interruption device 53, the battery pack 60, and the current measurement unit 54 are connected in series via power lines 55P and 55N. The power line 55P connects the positive external terminal 52 and the positive electrode of the battery pack 60. The power line 55N connects the negative external terminal 51 and the negative electrode of the battery pack 60.

[0044] The current interruption device 53 is provided on the positive power line 55P. The current measurement unit 54 is provided on the negative power line 55N.

[0045] A contact switch (mechanical) such as a relay or a semiconductor switch such as an FET can be used as the current interruption device 53. The current interruption device 53 is always controlled to be CLOSE. If an abnormality occurs in the battery 50, the current interruption device 53 is opened to cut off the current, thereby protecting the battery 50.

[0046] The current measurement unit 54 measures the current I [A] of the battery pack 60, and outputs a current measurement value Im to the control unit 120. The current measurement unit 54 may use a current detection resistor or a magnetic sensor.

[0047] The temperature sensor 58 is attached to the side of the battery pack 60 , measures the temperature of the battery pack 60 , and outputs the measured temperature to the control unit 120 .

[0048] The management device 100 is provided on the circuit board unit 65 (see FIG. 2). The management device 100 includes a voltage measurement unit 110 and a control unit 120. The control unit 120 is an example of an "estimation device."

[0049] The voltage measurement unit 110 is connected to both ends of each secondary battery cell 62 by a signal line, and measures the cell voltage V of each secondary battery cell 62. The voltage measurement unit 110 outputs to the control unit 120 the cell voltage V of each secondary battery cell 62 and the inter-terminal voltage VB of the battery pack 60 obtained by summing all of the voltages V.

[0050] The control unit 120 includes a CPU 121 having a calculation function, a memory 123 which is a storage unit, and a communication unit 125. The communication unit 125 is for communication with the vehicle ECU 30.

[0051] The control unit 120 monitors the measured current Im, total voltage VB, and temperature information of the battery pack 60 to monitor the state of the battery 50. In addition, the control unit 120 also monitors the cell voltage V of each secondary battery cell 62.

[0052] The memory 123 is a non-volatile storage medium such as a flash memory, an EEPROM, etc. The memory 123 stores a program for monitoring the state of the battery pack 60, a program for estimating the SOC (a program for executing the flow shown in FIG. 9), and data required for executing each program.

[0053] 2. Method for estimating the remaining charge of a battery pack In this embodiment, the secondary battery cell 62 contains lithium iron phosphate (LiFePO 4 ) is an LFP / Gr (iron phosphate) type lithium ion secondary battery cell that uses graphite as the negative electrode active material. Instead of connecting the twelve secondary battery cells 62 shown in Fig. 2 in three parallel and four series, four secondary battery cells 62 may be connected in series to form one assembled battery 60.

[0054] The same amount of current I flows through each of the secondary battery cells 62 constituting the battery pack 60, and the voltage VB of the battery pack 60 is the sum of the voltages V of the four secondary battery cells 62 connected in series. In the estimation of the remaining charge described below, the remaining charge of the battery pack 60 is estimated.

[0055] Description will be given using SOC as a physical quantity representing the remaining amount of electricity in the battery pack 60. SOC is the ratio [%] of the remaining capacity Cr [Ah] to the full charge capacity Co [Ah] of the battery pack 60, and is expressed by the following formula (1). The full charge capacity Co is the amount of electricity that can be discharged from the fully charged battery pack 60.

[0056] SOC = (Cr / Co) × 100 (1)

[0057] The current integration method is a method for estimating SOC based on the integrated value of current. As shown in the following formula (2), the current integration method estimates SOC based on the time integral value of current I. The sign of current I is positive when charging and negative when discharging.

[0058] SOC=SOCo+100×(∫Idt) / Co·····(2) SOCo is the initial value of SOC, I is the current, and t is the integration time.

[0059] As shown in the following formula (3), the current measurement value Im of the current measurement unit 54 includes a measurement error ε. Im = Ic + ε (3) Im is the measured current value, Ic is the true current value, and ε is the measurement error.

[0060] In the following description, the SOC estimated by the current integration method is referred to as the first SOC. In estimating the first SOC, the SOC error (SOC estimation error Se, described later) increases due to the accumulation of measurement error ε accompanying current flow. Gain error and offset error (error detected even in a state with no current) are known to be included in the measurement error ε. Since the gain error is offset by charging and discharging, the offset error is considered to be dominant.

[0061] The SOC estimation error Se can be expressed by the following equation (4) using the measurement error ε: The SOC estimation error Se is an example of a “cumulative error”.

[0062] Se=(∫εdt) / Co×100····(4)

[0063] The current integration method has a problem in that the measurement error ε accumulates, causing the SOC estimation error Se to increase over time. By correcting the first SOC estimated by the current integration method based on an SOC estimated by a method other than the current integration method, it is possible to reduce the SOC estimation error Se and improve the estimation accuracy of the first SOC.

[0064] One of the methods for estimating the SOC based on the voltage of the storage cell is the full charge detection method. In the full charge detection method, when the control unit 120 detects that the battery pack 60 has been charged to a voltage equivalent to a full charge, the SOC at that time is estimated to be 100% or a predetermined set value close to that. In the following description, the SOC estimated by the full charge detection method is referred to as the second SOC, and the second SOC when the battery pack 60 has been charged to a voltage equivalent to a full charge is referred to as 100%.

[0065] Whether the battery pack 60 has been charged to a voltage equivalent to full charge can be determined based on whether a predetermined full charge completion condition is met. For example, in the case of constant voltage charging, this can be determined by comparing the charging time Ts after the voltage VB of the battery pack 60 reaches a predetermined target voltage or the drooping current value with a threshold current Is (see FIG. 7). Whether the battery pack 60 has reached full charge may also be determined based on whether the total voltage VB of the battery pack 60 is equal to or greater than a predetermined value and the measured current value Im is equal to or less than a predetermined value.

[0066] In this embodiment, the first SOC estimated by the current integration method is corrected based on the second SOC estimated by the full charge detection method, and thereafter, the first SOC is estimated by the current integration method using the corrected first SOC as an initial value.

[0067] For example, if the full charge capacity is 60 [Ah] and the remaining capacity estimated by the current integration method just before the full charge detection is 59.528 [Ah], the remaining capacity is corrected from 59.528 [Ah] to 60 [Ah] after the full charge detection. After the correction, the remaining capacity of 60 [Ah] is set as the initial value and the first SOC is estimated by the current integration method. In other words, the first SOC is estimated with the initial value set to 100 [%].

[0068] The SOC difference Sx shown in the following formula (5) is the SOC difference obtained by subtracting the first SOC estimated by the current integration method from the second SOC estimated by the full charge detection method. Sx indicates the true value or a value close to the true value of the SOC estimation error Se by the current integration method. The SOC difference Sx is an example of a "remaining charge difference."

[0069] Sx=(2nd SOC-1st SOC)...(5)

[0070] For example, if the remaining capacity estimated using the current integration method immediately before detecting full charge is 59.528 [Ah], this is converted to the first SOC of 99.21 [%], so the SOC difference Sx is 100 [%] - 99.21 [%] = 0.79 [%].

[0071] A correction value Δε for the measurement error ε included in the current measurement value Im is calculated based on the SOC estimation error Se calculated using equation (4) and the SOC difference Sx calculated using equation (5) (equation (6) below).

[0072] Δε=k×(Se-Sx) / T (6) T is the current integration time, and k is a predetermined coefficient.

[0073] The current integration time T is the time for integrating the current measurement value Im when estimating the first SOC by the current integration method. Specifically, it is the time from the start of estimating the first SOC to immediately before detecting full charge.

[0074] Fig. 8 is an example of a graph plotting the change over time of the first SOC estimated value L0. In Fig. 8, the first SOC is corrected to 100% at t1, t2, and t3. In the first cycle, t0 to t1 is the current integration time T. In the second cycle, t1 to t2, and in the third cycle, t2 to t3 are the current integration time T. The dotted lines that sandwich the first SOC estimated value L0 indicate the range of the SOC estimation error Se, with the estimated value L0 at the center.

[0075] Using the correction value Δε calculated by equation (6), the measurement error ε of the current measurement value Im can be corrected as shown in the following equation (7).

[0076] ε1=ε-Δε (7) ε1 is the measurement error after compensation, and ε is the measurement error before compensation.

[0077] Correcting the measurement error ε improves the accuracy of the SOC estimation error Se. This improves the accuracy of the SOC estimation error Se, making it possible to narrow the SOC estimation range compared to when the measurement error ε is estimated to be larger than the true value.

[0078] 3. Control flow of SOC estimation process 9 is a flowchart of the SOC estimation process. The SOC estimation process is composed of steps S10 to S130, and is executed at a predetermined calculation cycle after the control unit 120 is started. It is assumed that the initial value SOCo of the first SOC and the initial value of the measurement error ε are stored in advance in the memory 123. The initial value of the measurement error ε is a statistical value or an experimental value. In the following example, the initial value of the measurement error ε is 4.8 [mA].

[0079] When the control unit 120 starts the SOC estimation process, it determines whether the battery pack 60 is fully charged or not based on the voltage VB of the battery pack 60 (S10). If the SOC does not satisfy the above-mentioned full charge completion condition, it determines that the battery pack 60 is not fully charged.

[0080] If the battery pack 60 is not fully charged (S10: NO), the control unit 120 estimates the first SOC of the battery pack 60 by a current integration method (S20). Specifically, as shown in formula (2), the control unit 120 integrates the current measurement value Im measured by the current measurement unit 54, and estimates the first SOC by adding or subtracting it from the initial SOC value SOCo. The control unit 120 stores the result in the memory 123.

[0081] For example, if the full charge capacity is 60 [Ah], the measured current value Im is 1 [A], the calculation cycle is 0.1 [s], the previous remaining capacity is 59.5 [Ah], and the first SOC is 99.17 [%], then the charge amount after 1000 cycles is 1 [A] x 0.1 [s] x 1000 / 3600 ≒ 0.028 [Ah]. Therefore, the updated value of the remaining capacity is 59.5 + 0.028 = 59.528 [Ah], and the updated value of the first SOC is 99.21 [%]. S20 is an example of a "first process" and a "first step".

[0082] Next, the control unit 120 calculates the SOC estimation error Se using the measurement error ε stored in the memory 123 (S30). The control unit 120 calculates the SOC estimation error Se based on equation (4) and stores the result in the memory 123.

[0083] For example, if the measurement error ε=4.8[mA] and the previous value of the SOC estimation error Se converted into capacity is 800[mAh], the accumulated error amount Cx accumulated after 1000 cycles is 800[mAh]+4.8[mA]×0.1×1000[s] / 3600≒800.13[mAh]. In this case, the updated value of the SOC estimation error Se is 800.13[mAh] / 60[Ah]×100≒1.33[%]. S30 is an example of a "second process" and a "second step".

[0084] Next, the control unit 120 judges the SOC estimation error Se (S40). Specifically, the absolute value of the SOC estimation error Se is compared with a threshold value TH1. The threshold value TH1 is an arbitrary value set according to the estimation accuracy required for the first SOC. If the SOC estimation error Se is smaller than the threshold value TH1 (S40: NO), the control unit 120 determines that it is not necessary to correct the first SOC. In this case, the process proceeds to S20, and the estimation of the first SOC using the current integration method continues.

[0085] As the integration time t becomes longer, the measurement error ε accumulates and the SOC estimation error Se becomes larger, and eventually exceeds the threshold value TH1.

[0086] When the absolute value of the SOC estimation error Se becomes equal to or greater than the threshold value TH1, the control unit 120 determines that the SOC estimation accuracy Se is large and that the measurement error ε needs to be corrected (S40: YES), and instructs the vehicle ECU 30 to charge the battery pack 60 (S50).

[0087] Even while the battery pack 60 is being charged, the control unit 120 continues to estimate the first SOC using the current integration method until the battery pack 60 satisfies the full charge completion condition, and stores the results one by one in the memory 123. When the full charge completion condition is satisfied, the control unit 120 determines that the battery pack 60 is fully charged (S10: YES).

[0088] Thereafter, the control unit 120 estimates the second SOC by a full charge detection method (S60). Specifically, the control unit 120 estimates the second SOC to be 100%. S60 is a process for estimating the SOC by a method (full charge detection method) different from the current integration method, and is an example of the "third process" and the "third step".

[0089] Next, the control unit 120 calculates the SOC difference Sx based on the formula (5) (S70).

[0090] When the first SOC immediately before the full charge detection is 99.21%, the SOC difference Sx is 0.79%. When the remaining capacity estimated by the current integration method immediately before the full charge detection is 59.528Ah, the capacity corresponding to the SOC difference Sx is 0.472Ah. S70 is an example of the "fourth process" and the "fourth step".

[0091] Next, the control unit 120 corrects the first SOC estimated by the current integration method based on the second SOC estimated by the full charge detection method (S80).

[0092] For example, if the full charge capacity is 60 [Ah] and the remaining capacity estimated value just before full charge detection using the current integration method is 59.528 [Ah], the remaining capacity estimated value is corrected to 60 [Ah] and the first SOC is corrected to 100 [%].

[0093] After the correction, the control unit 120 resets the SOC estimation error Se to zero (S90). In the above example, the SOC estimation error Se is reset to 1.33%. By resetting the SOC estimation error Se, the error accumulation amount Cx is also reset to 800.13 mAh.

[0094] Next, the control unit 120 subtracts the SOC difference Sx calculated in S70 from the SOC estimation error Se immediately before full charge detection calculated in S30 (S100).

[0095] In the above example, the SOC difference Sx is 0.79% and the SOC estimation error Se is 1.33%, so (Se-Sx) is 0.54%. In terms of capacity, 800.13mAh-0.472Ah is approximately 328mAh. S100 is an example of a "fifth process" and a "fifth step".

[0096] After that, the control unit 120 judges the magnitude of the absolute value of (Se-Sx). Specifically, the absolute value of (Se-Sx) is compared with a threshold value TH2 (S110). The threshold value TH2 is an arbitrary value set according to the accuracy required for the measurement error ε.

[0097] When the absolute value of (Se-Sx) is smaller than the threshold value TH2 (S110: NO), the control unit 120 determines that it is not necessary to correct the measurement error ε.

[0098] In this case, the process proceeds to S20 without correcting the measurement error ε. The control unit 120 estimates the first SOC by the current integration method using the measurement error ε stored in the memory 123. That is, the first SOC is estimated based on the formula (2) using the first SOC corrected in S80 as an initial value.

[0099] If the absolute value of (Se-Sx) is equal to or greater than the threshold value TH2 (S110: YES), the control unit 120 determines that the measurement error ε needs to be corrected. In this case, the control unit 120 calculates a correction value Δε for the measurement error ε using equation (6) based on the value of (Se-Sx) calculated in S100 (S120).

[0100] Next, the control unit 120 corrects the measurement error ε by equation (7) using the correction value Δε calculated in S120 (S130), and stores the corrected measurement error ε1 in the memory 123. S130 is an example of a "sixth process".

[0101] Then, the process proceeds to S20, where the control unit 120 estimates the first SOC by the current integration method using the corrected measurement error ε1. In this way, the estimation accuracy of the SOC estimation error Se can be improved.

[0102] <Example of determination in S110> In S110, the absolute value of (Se - Sx) is compared with a threshold TH2. When the absolute value of (Se - Sx) is greater than or equal to the threshold TH2, the control unit 120 determines that it is necessary to correct the measurement error ε. The threshold TH2 may be a fixed value or may be changed according to the current integration time T.

[0103] The measurement error ε can be expressed by the following equation (8) as the sum of the true error value ε0, which is the true value of the error, and the error amount εx. ε = ε0 + εx ····· (8)

[0104] Hereinafter, when it is desired to suppress the error amount εx included in the measurement error ε to less than 0.5 [mA], it will be explained how the determination is made when the current integration time T is 31 days and 7 days, respectively.

[0105] When the error amount εx is 0.5 [mAh], when the absolute value of the error (Se - Sx) that accumulates with the integration time is converted to capacitance, it is 0.5 [mA] × 24 [h] = 12 [mAh] per day. Therefore, in S110, if the error per day is less than 12 [mAh], no correction is performed, and if it is 12 [mAh] or more, correction is performed. At this time, the threshold TH2, when converted to the SOC per day, is 12 [mAh] / (60 [Ah] × 1000) × 100 = 0.02 [%].

[0106] For example, when the capacitance conversion value of the error (Se - Sx) is 328 [mAh] and the current integration time T at this time is 31 days, the error per day is 328 [mAh] / 31 [days] ≈ 10.6 [mAh]. Since this is less than 12 [mAh], the control unit 120 does not perform correction (S110: NO).

[0107] When the current integration time T required for the same 328 [mAh] error to accumulate is 7 days, the error per day is 46.9 [mAh], which is 12 [mAh] or more. In this case, the control unit 120 determines that correction is necessary (S110: YES) and executes S120 and S130.

[0108] <Correction Example of S130> When it is determined in S110 that correction is necessary, the measurement error ε is corrected. As the correction value Δε of the measurement error ε, the value calculated by Expression (6) in S100 is used. The coefficient k is a positive value of 1 or less. If k = 1, the measurement error ε can be corrected with a large correction value Δε. As a positive value less than 1 for the coefficient k, correction with a small correction value Δε may be repeated.

[0109] As in the above example, consider the case where a large SOC estimation error Se of 328 [mAh] was estimated in 7 days. In this case, assuming a constant current and converting the capacity to current, it becomes 328 [mAh] / 168 [h] = 1.95 [mA]. This is the error amount εx included in the measurement error ε.

[0110] When the previous value of the measurement error ε is 4.8 [mA], when the coefficient k = 1, the error amount εx directly becomes the correction value Δε. From Expressions (6) and (7), the corrected measurement error ε1 = 4.8 [mA] - 1.95 [mA] = 2.85 [mA].

[0111] Therefore, in S130, by replacing the measurement error ε of the current measurement value Im from the previous value of 4.8 [mA] with the corrected value of 2.85 [mA], the estimation accuracy of the SOC estimation error Se in the current integration method can be improved.

[0112] When a positive value less than 1 is used as the coefficient k, the following occurs.

[0113] For example, when the coefficient k is set to 0.5, since it is 4.8 [mA] - 1.95 [mA] × 0.5 = 3.825 [mA], the corrected measurement error ε1 is set to 3.825 [mA]. Compared with the case where k = 1, the correction value Δε is smaller. When performing the full charge detection method in the future, correction is performed and the correction is repeated to gradually bring the measurement error ε of the current closer to the true error value ε0.

[0114] 5. Explanation of Effects In this configuration, the estimation accuracy of the SOC estimation error Se is improved by correcting the measurement error ε included in the current measurement value Im, thereby making it possible to narrow the SOC estimation range Y. If the measurement error ε before correction is estimated to be smaller than the true value, correcting the measurement error ε improves the estimation accuracy of the SOC estimation error Se and improves the reliability of the SOC estimation range Y.

[0115] Figure 10 is a graph showing the SOC estimation range. L0 is the estimated SOC value, Y1 is the SOC estimation range without correction, and Y2 is the SOC estimation range with correction. By correcting the measurement error ε, the estimation error Se can be suppressed, so the SOC estimation range Y can be narrowed compared to when no correction is performed.

[0116] Narrowing the estimated SOC range Y makes it possible to maintain battery performance. For example, in charging control of the battery pack 60, the charging current may be determined according to the upper limit of the estimated SOC range Y in order to prevent deterioration of battery performance. In this configuration, the battery pack 60 can be charged with an appropriate charging current according to the upper limit of the estimated SOC range Y, thereby maintaining battery performance.

[0117] When the SOC usage range (e.g., SOC 50% to 80%) is determined, the battery pack 60 can be charged until the upper limit value of the SOC estimation range Y reaches the upper limit value of the usage range. In this configuration, the SOC estimation range Y is narrowed and L0 can be brought close to the upper limit value of the usage range, so that the performance of the battery pack 60 can be utilized.

[0118] By correcting the measurement error ε, the time until the SOC estimation error Se, which is the accumulation of the measurement error ε, reaches the threshold value TH1 can be extended, and the frequency of SOC correction using the full charge detection method can be reduced.

[0119] By reducing the frequency of SOC correction, the frequency of charging for SOC correction can be reduced. Because regenerative power cannot be accepted during charging to full charge, reducing the frequency of charging for SOC correction makes it possible to shorten the period during which regenerative power acceptance is restricted, which contributes to improving the fuel efficiency of the vehicle.

[0120] <Embodiment 2> In the first embodiment, the measurement error ε is corrected using the second SOC estimated by the full charge detection method.

[0121] In the second embodiment, the measurement error ε is corrected using the second SOC estimated by the OCV method.

[0122] 11 shows the correlation characteristic of SOC-OCV of an LFP / Gr type lithium ion secondary battery cell 62 that uses lithium iron phosphate for the positive electrode and graphite for the negative electrode. The horizontal axis is SOC and the vertical axis is OCV. OCV is open circuit voltage. OCV may be the terminal voltage of the cell 62 when there is no current or when it can be considered that there is no current (when the current value is below a predetermined value).

[0123] A lithium ion secondary battery cell has a plurality of charging regions including a low change region L where the change in OCV relative to the change in SOC is relatively low, and a high change region H where the change is relatively high.

[0124] Specifically, it has two low change regions L1, L2 and three high change regions H1, H2, H3.

[0125] The low change region L1 is in the range of 35[%] to 62[%] in terms of SOC value, and the low change region L2 is in the range of 68[%] to 96[%] in terms of SOC value.

[0126] The low change regions L1 and L2 are plateau regions where the change in OCV relative to the change in SOC is very small and the OCV is almost constant. The plateau region is a region where the change in OCV relative to the change in SOC is equal to or less than a predetermined value. The predetermined value is, for example, 2 [mV / %].

[0127] The first high change region H1 is the range of SOC values ​​greater than 62% and less than 68%, the second high change region H2 is the range of SOC values ​​less than 35%, and the third high change region H3 is the range of SOC values ​​greater than 96%.

[0128] The OCV method estimates the SOC by referring to the SOC-OCV correlation characteristic (graph in FIG. 11) for the OCV. For example, when the OCV is OCVx, the SOC can be estimated as SOCx. In this way, the second SOC can be estimated by the OCV method.

[0129] The usage range F of the battery pack 60 may be set to an upper limit less than 100%, such as 50% to 80%. By setting the upper limit of the usage range F to less than 100%, allowing for a margin relative to full charge, regeneration can be accepted.

[0130] In this example, the first high change region H1 is included in the usage range F. Therefore, even within the usage range F, the OCV method can be performed to estimate the second SOC.

[0131] The OCV method may be performed not only within the usage range F, but also by charging the battery pack 60 up to the third high change region H3, or by discharging the battery pack 60 up to the second high change region H2.

[0132] <Other embodiments> The present invention is not limited to the embodiments described above and in the drawings. For example, the following embodiments are also included within the technical scope of the present invention. Furthermore, in addition to the embodiments described below, various modifications can be made without departing from the spirit of the present invention.

[0133] (1) In the above embodiment, a lithium ion secondary battery cell is shown as an example of the secondary battery cell 62. The secondary battery cell 62 is not limited to a lithium ion secondary battery cell, and may be another non-aqueous electrolyte secondary battery cell. A lead storage battery cell may also be used. A capacitor may be used instead of the secondary battery cell. The secondary battery cell 62 and the capacitor are examples of "electricity storage cells".

[0134] (2) The battery pack 60 is not limited to a configuration in which a plurality of secondary battery cells 62 are connected in series and parallel, but may be a series connection or a single cell configuration.

[0135] (3) In the above embodiment, the battery 50 is for an automobile, but it may be for a motorcycle. The battery 50 may be used for other moving objects such as ships, AGVs, and aircraft.

[0136] (4) In the above embodiment, the control unit 120 is provided inside the battery 50. The control unit 120 may be provided outside the battery 50. In other words, the control unit 120 provided outside the battery 50 may correct the measurement error ε, calculate the SOC estimation error Se, and estimate the SOC. In this case, the control unit 120 may acquire information on the current measurement value Im and the total voltage VB from the current measurement unit 54 and the voltage measurement unit 110 provided inside the battery 50 via communication, and may correct the measurement error ε, calculate the SOC estimation error Se, and estimate the SOC.

[0137] (5) In the above embodiment, the full charge detection method and the OCV method are exemplified as methods for estimating the remaining charge amount that are different from the estimation based on the integrated value of the current. However, any method other than the full charge detection method and the OCV method may be used as long as it is possible to estimate the remaining charge amount without using the integrated value of the current. [Explanation of symbols]

[0138] 10 Automobiles (examples of vehicles) 50 Battery (an example of an energy storage device) 54 Current measurement section 60 Battery pack 62 Secondary battery cell (an example of a storage cell) 110 Voltage measurement section 120 Control unit (an example of an estimation device) ε Measurement error Δε correction value Im Current measurement value Se SOC error (an example of cumulative error) Sx SOC difference (example of remaining charge difference)

Claims

1. An estimation device for estimating a remaining amount of electricity in a storage cell or a battery pack, A first process of estimating a remaining amount of electricity based on an integrated value of a current of the storage cell or the assembled battery; A second process of estimating a cumulative error of a remaining amount of electricity based on an integrated value of the measurement error of the current; A third process for estimating a remaining amount of electricity by a method different from the first process; A fourth process of calculating a remaining electric quantity difference between the remaining electric quantity estimated in the first process and the remaining electric quantity estimated in the third process; a fifth process of calculating a correction value of the measurement error based on a difference between the accumulated error and the remaining electric quantity difference and a current integration time; A sixth process is executed to correct the measurement error based on the correction value calculated in the fifth process. and an estimation device that, after executing the sixth process, executes the second process using the corrected measurement error.

2. The estimation device according to claim 1, and an estimation device that performs the sixth process to correct the measurement error when a difference between the accumulated error and the remaining electric quantity difference exceeds a threshold value.

3. The estimation device according to claim 1 or 2, In the third process, the estimation device estimates a remaining amount of electricity in the storage cell or the assembled battery by a full charge detection method in which the storage cell or the assembled battery is charged until fully charged.

4. A power storage device, The storage cell or the assembled battery; a current measuring unit that measures a current of the storage cell or the assembled battery; A power storage device comprising: the estimation device according to any one of claims 1 to 3.

5. A method for estimating a remaining amount of electricity in a storage cell or a battery pack, comprising: A first step of estimating a remaining amount of electricity based on an integrated value of a current of the storage cell or the assembled battery; A second step of estimating a cumulative error of a remaining amount of electricity based on an integrated value of the measurement error of the current; A third step of estimating a remaining amount of electricity by a method different from that of the first step; a fourth step of calculating a remaining charge difference between the remaining charge calculated in the first step and the remaining charge calculated in the third step; a fifth step of calculating a correction value for the measurement error based on a difference between the accumulated error and the remaining electric quantity difference and a current integration time; A sixth step of correcting the measurement error based on the correction value calculated in the fifth step; the estimation method further comprising: executing the second step using the corrected measurement error after executing the sixth step.

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